Although both $\mathrm{CO}_2$ and $\mathrm{H}_2 \mathrm{O}$ are triatomic molecules, the shape of $\mathrm{H}_2 \mathrm{O}$ molecule is bent while that of $\mathrm{CO}_2$ is linear. Explain this on the basis of dipole moment.

Question

Although both $\mathrm{CO}_2$ and $\mathrm{H}_2 \mathrm{O}$ are triatomic molecules, the shape of $\mathrm{H}_2 \mathrm{O}$ molecule is bent while that of $\mathrm{CO}_2$ is linear. Explain this on the basis of dipole moment.,

MARKS App · Accepted Answer

The dipole moment studies show that net dipole moment of $\mathrm{CO}_2$ molecule is zero. This is possible only if $\mathrm{CO}_2$ is a linear molecule $(\mathrm{O}=\mathrm{C}=\mathrm{O})$ so that dipole moments of $\mathrm{C}-\mathrm{O}$ are equal and opposite and hence cancel out. On the other hand, $\mathrm{H}_2 \mathrm{O}$ molecule is found to have a net dipole moment $(1.84 \mathrm{D})$ though it contains $2 \mathrm{O}-\mathrm{H}$ bonds. This shows that it is a bent molecule.

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